The present invention relates to a stolen article detection tag sheet attached to an article in, e.g., a department store, and a method for manufacturing the same.
FIG. 1A is a plan view of a conventional stolen article detection tag sheet, and FIG. 1B is a sectional view of the tag sheet taken along the line I--I of FIG. 1A. The tag sheet has conductive pattern 12 formed on insulating sheet 10 of, e.g., a polyimide resin. Pattern 12 is obtained by selectively etching a metal film, e.g., a copper foil, formed to cover the entire surface of sheet 10. Pattern 12 has sections 12A, 12B, and 12C serving as a receiving antenna, a transmitting antenna, and an inductor, respectively. Semiconductor diode device 14 is connected to two ends of portion 12C through solder 16. Diode device 14 and portion 12C constitute an LC resonator. This tag sheet is electrically equivalent to the circuit shown in FIG. 1C. Pattern 12 and diode device 14 are covered with, e.g., resin insulating film 18 by means of thermo compression bonding and are protected by it.
In a shoplifting prevention system of a shop such as a department store, a detector shown in FIG. 2 is used together with a tag sheet in order to find a stolen article. Printing is performed on the tag sheet and the printed tag sheet is attached to an article as, e.g., a price tag or an article tag. All articles are displayed in this state for sale in the store. When a customer selects a desired article and pays for it at a cashier counter, a tag sheet on the article is removed from the article by the cashier. The detector is installed at an appropriate exit of the shop. When someone puts on, e.g., a jacket with attached tag sheet TG and is departing through the exit, as shown in FIG. 2, the detector sets off an alarm, indicating that shoplifting has occurred. The detector comprises transmitter 20 for continuously generating a high-frequency signal of about, e.g., 1.15 GHz, receiver 22 for detecting a high-frequency signal of 2.3 GHz, and transmitting and receiving antennas 24 and 26, e.g., opposing each other sandwiching an exit doorway. A signal generated by transmitter 20 is supplied to transmitting antenna 24 and is radiated from antenna 24 as a radio wave. The radio wave is input to tag sheet TG attached to the article passing the exit doorway. Receiving antenna 26 supplies a high-frequency signal corresponding to the input radio wave to receiver 22. Receiver 22 turns on an alarm in response to a 2.3-GHz high-frequency signal. The transmitting/receiving frequency of tag sheet TG is predetermined by specifying the constant of the LC resonator, i.e., the product of the inductance of section 12C and the parasitic capacitance across the two ends of diode device 14.
However, the conventional tag sheet has the following problems.
First, polyimide is used as a material for insulating sheet 10 and, during a process of forming conductive pattern 12, a copper foil is formed on the entire surface of one major surface of sheet 10 and then selectively removed by etching. Polyimide and copper foil are relatively expensive, and a manufacturing process including etching is comparatively complex. Therefore, a tag sheet of this type requires high material and manufacturing costs and is not suitable for mass production.
Second, mold-packaged diode device 14 is fixed on insulating sheet 10. Because of this, it is difficult to manufacture a thin tag sheet which is inherently needed for the application. Since diode device 14 is located on part of the surface of sheet 10, after device 14 is covered, the tag sheet cannot have a flat surface. Thus, the surface of the tag sheet is not suitable for printing, e.g., an article name on it.
Third, diode device 14 is connected to conductive pattern 12 through solder 16 over insulating sheet 10. Connection by means of a solder can easily be influenced by a fluctuation in the manufacturing process, and a good connection state cannot often be stably obtained.